1. Field of the Invention
The object of the invention is a method for the manufacture of aluminum trihydrate (Al(OH)3 by means of hydrolysis of aluminum alcoholates in aqueous, alkaline solution with addition of organic compounds, the so-manufactured aluminum trihydrates and their use as catalyst supports.
2. Description of the Prior Art
In general three aluminum trihydroxide modifications are known, in the following called “aluminum trihydrate”: Al(OH)3, β-Al(OH)3 and γ-Al(OH)3.
α-Al(OH)3 (hydrargillite, gibbsite) is a natural product occurring as bauxite. It finds its principal industrial use as an input product of industrial purity in the winning of aluminum (bauxite decomposition) and as an inexpensive starting material for manufacture of sodium aluminate.
Due to its high level of impurities naturally occuring bauxite is not suitable as a catalyst support.
β-Al(OH)3 known as bayerite can be prepared by salt precipitation from aluminum sulfate and sodium aluminate solution or through hydrolysis of aluminum alcoholate. The latter variant is suitable, for preparing high purity bayerite while from the salt precipitation sodium and sulfate contaminated products precipitate. The high purity bayerite and its secondary product obtained by calcining find industrial application in the manufacture of catalyst supports. Due to the crystalline nature (crystallite size of 30 to 40 nm measured at the 311-reflex) this mistrial is not dispersable and consequently hard to process to paste-like masses for manufacture of extrudates, such as are employed in the manufacture of catalyst supports.
The manufacture of γ-Al(OH)3, also called nordstrandite, is likewise known. Due to the only small differences in the physical characteristics to bayerite, nordstrandite has no special technical significance. There is also the fact that the synthesis is not economical due to higher amounts of wash water is from a technical standpoint questionable environmentally and through the duration of the synthesis being more than 3 days.
Aluminum hydroxides are manufactured by means of precipitation from aqueous solutions by utilization of a precipitation aid and other ways. Thus U.S. Pat. No. 5,928,127 describes precipitation of an aluminum oxide sol from an aqueous solution by addition of sulfonic acids.
From DE 195 22 946 furthermore a method is known for the manufacture of a finely divided aluminum hydroxide by reaction of aluminum alkoxides with other metal oxides at high shear stirring rates.
The known methods up to now for the manufacture of aluminum hydroxides have the disadvantage that the aluminum hydroxides obtained are not sufficiently pure for the manufacture of catalyst supports or are not available in a uniform modification.